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manpages-dev_2.62-1_all 
NAME
sched_rr_get_interval - get the SCHED_RR interval for the named process
SYNOPSIS
#include <sched.h>
int sched_rr_get_interval(pid_t pid, struct timespec *tp);
DESCRIPTION
sched_rr_get_interval() writes into the timespec structure pointed to
by tp the round-robin time quantum for the process identified by pid.
The timespec structure has the following form:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
If pid is zero, the time quantum for the calling process is written
into *tp. The identified process should be running under the SCHED_RR
scheduling policy.
POSIX systems on which sched_rr_get_interval() is available define
_POSIX_PRIORITY_SCHEDULING in <unistd.h>.
On success, sched_rr_get_interval() returns 0. On error, -1 is
returned, and errno is set appropriately.
ERRORS
EFAULT Problem with copying information to userspace.
EINVAL Invalid pid.
ENOSYS The system call is not yet implemented (only on rather old ker‐
nels).
ESRCH The process whose ID is pid could not be found.
POSIX.1-2001.
NOTES
Linux Notes
POSIX does not specify any mechanism for controlling the size of the
round-robin time quantum. However, Linux provides a (non-portable)
method of doing this. The quantum can be controlled by adjusting the
process’s nice value (see setpriority(2)). Assigning a negative (i.e.,
high) nice value results in a longer quantum; assigning a positive
(i.e., low) nice value results in a shorter quantum. The default quan‐
tum is 0.1 seconds; the degree to which changing the nice value affects
the quantum has varied somewhat across kernel versions.
sched_setscheduler(2) has a description of the Linux scheduling scheme.
Programming for the real world - POSIX.4 by Bill O. Gallmeister,
O’Reilly & Associates, Inc., ISBN 1-56592-074-0